The present invention relates to a color video camera using a solid-state image pickup device and, more particularly, to a signal processing apparatus for arithmetically operating a plurality of signals which are output from an image pickup device having a number of small color separation optical filters, thereby producing color signals.
Recently, home-use VTRs have widely been used and in association of this widespread use, the need is more and more increasing for the color video camera which can be used together with the home-use VTR and for the integrated color video camera which is constructed integrally with the VTR. In such color video cameras, it is necessary not only to satisfy the fundamental performances such as high sensitivity and high picture quality but also to satisfy the requirements for small size and low price. For this purpose, the single tube type or single plate type color video camera in which only one image pickup tube or solid-state image pickup device is used in the image pickup section is the main current.
In such a single tube type or single plate type color video camera, small color separation optical filters which can transmit different color lights are regularly arranged on the photo sensing surface of the image pickup tube or solid-state image pickup device (hereinafter, generally referred to as the image pickup device), the respective signals corresponding to the color separation optical filters are arithmetically operated, and the luminance signal and chrominance signal in accordance with the television system are produced. In this case, as the color separation optical filter, the filters of what is called a complementary color system which can respectively transmit the yellow, cyan, and transparent lights whose light transmission amounts are large are more advantageous to realize high sensitivity rather than the filters of primary color lights (namely, red, green, and blue) whole light transmission amounts are small.
However, in the color video camera having the image pickup device provided with such color separation optical filters (hereinafter, referred to as color filters), when an image of an object of a fine picture pattern is picked up, a pseudo signal called an aliasing is produced, causing the picture quality to remarkably deteriorate. The aliasing is the beat interference which is caused by the sampling of the video signal due to the picture elements array corresponding to the respective color filters.
As the technique to suppress such an aliasing there is proposed a method disclosed in, for example, "SINGLE-CHIP COLOR CAMERAS WITH REDUCED ALIASING", International Electronic Imaging Exposition & Conference, the advance printing of paper summaries, pages 43-48, Oct. 7-10, 1985, Electronic Imaging '85. According to this method, the aliasing which is caused in the luminance signal (this aliasing is called the luminance aliasing) is suppressed by use of a luminance matrix. On the other hand, the aliasing (called the color aliasing) is also similarly generated in the color signal at the spatial frequency of the picture pattern which corresponds to 1/2 of the sampling frequency according to the arrangement of color filters. To reduce this color aliasing, for example, a method as disclosed in Japanese Patent Laid-Open No. 198978/83 (corresponding U.S. application Ser. No. 494,449) is proposed. According to this method, the optical low pass filter consisting of two birefringence plates such as crystal plates and the 1/4 wavelength plate and the like are combined, thereby reducing the response of the spatial frequency band of the incident light in which the aliasing will be generated.
Although the luminance aliasing can be suppressed by the aliasing suppressing means using the luminance matrix mentioned above, the color aliasing cannot be reduced. The color aliasing becomes, in particular, a large obstacle in the case of the system using the color filters of the complementary color system which are used to improve the sensitivity. If two crystal filters mentioned above are used to reduce the color aliasing the response to the necessary signal will be also simultaneously reduced. Thus, the resolution deteriorates and it is difficult to obtain a high picture quality as the fundamental performance. In addition, since the crystal filter is expensive, there is the problem such that it doesn't meet the object to provide a cheap homeuse camera.